Organic el element

ABSTRACT

In order to prevent shorts between anode and cathode by dielectric breakdown in an organic EL element, the organic EL layer includes a leak prevention layer that takes on a high resistance when its temperature is increased.

TECHNICAL FIELD

The present invention relates to organic electroluminescent elements.

BACKGROUND ART

Organic EL (electroluminescent) elements having a structure in which anorganic functional layer is sandwiched between an anode and a cathodeare known as one type of light-emitting thin film elements.

FIG. 1 is a cross-sectional view showing an example of a conventionalorganic EL element 100. The organic EL element 100 includes a substrate110, an anode 120 formed on the substrate 110, an organic functionallayer 140 made of a plurality of layers laminated on the anode 120, anda cathode 130 formed on the organic functional layer 140.

The organic functional layer 140 is a functional layer including atleast a light-emitting layer. In FIG. 1, the organic functional layer140 includes a hole injection layer 141, a hole transport layer 142, alight-emitting layer 143, and an electron injection layer 144, layeredin this order on top of the anode 120.

When a voltage is applied between the anode 120 and the cathode 130,holes are injected into the light-emitting layer 143 via the holetransport layer 142 from the anode 120 or the hole injection layer 141,while at the same time electrons are injected into the light-emittinglayer 143 from the cathode 130 or the electron injection layer 144.Inside the light-emitting layer 143, the holes and electrons recombine,forming excitons. Within an extremely short time, the excitons fall to alower energy level, and some emit the energy difference between thelower energy level and the excited state as light. The light given offwithin this light-emitting layer 143 is emitted to the side of thesubstrate 110 or to the side of the cathode 130. Thus, the organic ELelement 100 functions as a light-emitting element.

However, when there are defect locations in this conventional organic ELelement, such as pinholes or partially thinner film thickness, then theresistance at those defect locations becomes lower than at otherportions, and current (electrons or holes) concentrates at those defectlocations. This results in the problem that the buildup of Joule heatand the increase in the strength of the electric field due to suchconcentrations causes dielectric breakdown at the defect locations, andultimately leads to shorts between the anode and the cathode.

FIGS. 2A and 2B illustrate this dielectric breakdown due to defects.This organic EL element 200 is fabricated by forming an anode 220 on asubstrate 210, then forming an organic functional layer 230 and anorganic functional layer 240, followed by forming a cathode 250. In theorganic EL element 200 in FIG. 2A, a pinhole 245, which is a defect, hasdeveloped in the organic functional layer 240 during the film formationprocess, and this pinhole 245 is filled by the cathode 250.

When a voltage is applied to this organic EL element 200 having such adefect, current concentrates at a portion 235 within the organicfunctional layer 230 located directly below the pinhole 245 resulting ina large electric field. When this state continues, dielectric breakdownoccurs in the portion 235 within the organic functional layer 220, asshown in FIG. 2B, the anode 220 and the cathode 250 are shorted, and theorganic EL element 200 cannot function as a light-emitting elementanymore. When an organic EL element having such a defect is used for adisplay panel or the like, the display quality of the display panel isseverely damaged, and its value as a product is diminished.

The above-described defect tends to occur in particular when organicfunctional layers are formed by a vapor deposition process. Ordinarily,vapor deposition processes have poor step coverage (i.e. ability tocover steps), so that film defects are easily incurred by scratches inthe substrate or foreign matter on the substrate.

One of the issues addressed by the present invention is the problem thatshorts occur between anode and cathode due to dielectric breakdown, asdescribed above.

DISCLOSURE OF THE INVENTION

An organic EL element according to one aspect of the present inventionincludes an anode, a cathode, and a light-emitting organic EL layersandwiched between the anode and the cathode, and includes at least aleak prevention layer that takes on a high resistance when itstemperature is increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of an organic EL element.

FIGS. 2A and 2B are diagrams illustrate a problem of organic ELelements.

FIG. 3 is a diagram showing an embodiment of the organic EL elementaccording to the present invention.

FIGS. 4A and 4B are diagrammatic views illustrating the effect of theleak prevention layer.

FIGS. 5A and 5B are graphs illustrating the resistance of the leakprevention layer as a function of temperature.

FIGS. 6A and 6B are diagrams showing the after-treatment for improvingthe step coverage of a leak prevention layer formed by vapor depositionor the like.

FIG. 7 is a diagram showing a modified embodiment of the organic ELelement according to the present invention.

FIG. 8 is a diagram showing another modified embodiment of the organicEL element according to the present invention.

FIG. 9 is a graph showing the relation between the heating temperatureand the specific resistance of a polyaniline film.

FIG. 10 is a diagram showing the inverse voltage characteristics oforganic EL elements.

EMBODIMENTS OF THE INVENTION

The following is a detailed description of embodiments of an organic ELelement according to the present invention.

An organic EL element according to the present invention is providedwith a light-emitting organic EL layer, sandwiched between an anode anda cathode. This organic EL layer includes at least a leak preventionlayer that takes on a high resistance when its temperature is raised.The following is a more detailed explanation of an organic EL elementaccording to this embodiment, with reference to the accompanyingdrawings.

FIG. 3 is a cross-sectional view showing an organic EL element 10 as anembodiment of the present invention. This organic EL element 10 includesa substrate 11, an anode formed on the substrate 11, an organicfunctional layer 14 made of a plurality of layers layered on the anode12, and a cathode 13 formed on the organic functional layer 14.

The organic functional layer 14 includes, in order from the side of theanode 13, a hole injection layer 15, a hole transport layer 16, alight-emitting layer 17, and an electron injection layer 18. When avoltage is applied, the hole injection layer 15 injects holes via thehole transport layer 16 into the light-emitting layer 17. And when avoltage is applied, the electron injection layer 18 injects electronsinto the light-emitting layer 17. Within the light-emitting layer 17,the holes and electron recombine, forming excitons. Within an extremelyshort time, the excitons fall to a lower energy level, and some emit theenergy difference between the lower energy level and the excited stateas light. The light given off within this light-emitting layer 17 isemitted to the side of the substrate 11 or to the side of the cathode13. Thus, the organic EL element 10 functions as a light-emittingelement.

Within an ordinary working temperature region, the hole injection layer15 functions as a hole injection layer injecting holes via the holetransport layer 16 into the light-emitting layer 17. On the other hand,in a temperature region that is higher than the ordinary workingtemperature region, it functions as a leak prevention layer thatsuppresses excessive currents. The hole injection layer 15 is made of amaterial whose specific resistance increases at least in a hightemperature region that exceeds the maximum working temperature of theproduct (maximum operating temperature or maximum storage temperature),thus taking on a high resistance. Consequently, the hole injection layer15 takes on a high resistance as a result of the generation of Jouleheat due to current concentration caused by defects. Thus, the currentis curbed, and the element can be protected from such damage asdielectric breakdown.

FIGS. 4A and 4B are diagrammatic views illustrating the effect of theleak prevention layer. Here, to simplify the explanations, the organicfunctional layer is shown as being made only of two layers, namely theleak prevention layer and the other layers.

In FIG. 4A, the organic EL element 20 is fabricated by forming an anode22 on a substrate 21, then forming a leak prevention layer 23 and anorganic functional layer 24, followed by forming a cathode 25. Here, theleak prevention layer 23 is made of a material whose specific resistanceincreases at least in a high temperature region that exceeds the maximumworking temperature of the product (maximum operating temperature ormaximum storage temperature), thus taking on a high resistance.Furthermore, in this organic EL element 20, there is a pinhole 24 a,which is a defect, formed during the film formation process in theorganic functional layer 24, and this pinhole 24 a is filled up by thecathode 25.

When voltage is applied to the organic EL element 20 having such adefect, current concentrates at a portion 23 a within the leakprevention layer 23 that is located directly below the pinhole 24 a,resulting in a large electric field. This current concentration causes alarge Joule heat, which increases the temperature of the leak preventionlayer beyond the maximum working temperature. As shown in FIG. 4B, thistemperature increase causes the specific resistance of the leakprevention layer 23 to rise, so that the leak prevention layer 23 takeson a high resistance. Consequently, the current flowing in the leakprevention layer 23 is decreased, lessening the heat generation and theelectric field in the leak prevention layer (thermal repair). Thus, byproviding a layer functioning as a leak prevention layer as one layer ofthe organic functional layer, current concentrations at one locationwithin the organic functional layer can be prevented, and breakdown ofthe organic EL element 20 can be prevented.

In FIG. 3, the hole injection layer 15 was configured as a leakprevention layer, but the leak prevention layer may be provided at anyposition of the organic functional layer. As mentioned before, the leakprevention layer does not only prevent current concentrations, but mayalso perform a part of the functions of the organic EL element duringordinary operation, such as injection or transport of carriers(electrons or holes). Consequently, in order to increase the elementefficiency of the overall organic EL element, it is necessary toappropriately set the ionization potential, the carrier mobility etc. inaccordance with the location where it is placed. For example, a leakprevention layer that is arranged closer to the cathode than thelight-emitting layer needs to have high electron transport abilities,and a leak prevention layer that is arranged closer to the anode thanthe light-emitting layer needs to have high hole transport abilities.

The layers other than the leak prevention layer are made of alow-molecular weight material, and if the leak prevention layer is madeby a wet film formation process, such as spin-coating or printing, or bya film formation process causing considerable damage to the substrate,such as sputtering, then it is preferable that the leak prevention layeris formed first. Ordinarily, organic materials of low molecular weighthave a low resistance to solvents and a low heat resistance.Consequently, when the organic functional layers other than the leakprevention layer, which are made of organic materials of low molecularweight, are formed, and then the leak prevention layer is formed by oneof the above-mentioned processes, then there is the possibility that theorganic functional layers other than the leak prevention layer aredamaged.

More concretely, in the case of an organic EL element in which the anodeis arranged on the substrate, it is preferable that a leak preventionlayer with hole transport capability is formed directly on the anode.And in the case of an organic EL element in which the cathode isarranged on the substrate, it is preferable that a leak prevention layerwith electron transport capability is formed directly on the cathode.

It is preferable that the leak prevention layer is increased takes on ahigh resistance at temperatures above 120° C. The working temperaturerange of ordinary organic EL elements is up to about 100° C., so that itbecomes possible to inhibit failure of the element due to currentconcentrations by letting it take on a high resistance at temperatureshigher than that.

Furthermore, it is even more preferable that the leak prevention layertakes on a high resistance at temperatures above 200° C. Even though theworking temperature range of organic EL elements is up to about 100° C.,the organic EL element may become 120 to 200° C. during use, due toJoule heat generated by the current flowing through the organic ELelement and heat generation from locations outside the organic ELelement, such as driving circuitry. Thus, in order to not hinder thedriving of the organic EL element during ordinary operation, it isbetter not to let it take on a high resistance up to 200° C.

It is preferable that the leak prevention layer takes on a highresistance at temperatures less than 400° C., and it is even morepreferable that it takes on a high resistance at temperatures less than300° C. When examining portions where a short has developed betweenanode and cathode in conventional organic EL elements, it can be seenhow the Al used for the cathode has melted, so that it seems that defectportions occur where the temperature has risen locally and temporarilyto the melting point of Al (about 660° C.). Ordinarily, in hightemperature regions, such as above 500° C., the leak prevention layeritself is decomposed, and its weight is reduced fast, so that it losesthe capability to prevent shorts. Consequently, it is not preferablethat the taking on of a high resistance by the leak prevention layeroccurs at temperatures at which it is not helpful in order to preventshorts. Ordinarily, it is effective that it takes on a high resistancein a temperature region of about 300 to 400° C.

In conclusion, it is preferable that the leak prevention layer takes ona high resistance at temperatures of 120 to 400° C., and it is even morepreferable that it takes on a high resistance at temperatures of 200 to300° C.

FIGS. 5A and 5B are graphs illustrating the resistance of the leakprevention layer as a function of temperature. Here, it is preferablethat the resistance of the leak prevention layer exhibits a steep rateof change in the region of temperatures at which it takes on a highresistance. When the change in the region of temperatures at which ittakes on a high resistance (region in which high resistance is taken on)is smooth as in FIG. 5A, then the lessening of the current at the defectportions proceeds slowly, so that the influence of the Joule heatextends to the areas around the defect portions. Ideally, the leakprevention layer acts as a fuse in the defect portions, and it isdesirable that the resistance of the leak prevention layer increasessharply in the region of temperatures at which a high resistance istaken on, as in FIG. 5B.

Here, that the leak prevention layer takes on a high resistance meansthat Joule heat due to current concentrations increases the resistanceof the leak prevention layer considerably to an extent at which noshorts occur between the electrodes. When a defect portion has assumed ahigh temperature due to current concentration, the resistance of theleak prevention layer alone needs to be increased to a resistanceequivalent to that of the entire organic functional layer of a normalportion, in order to lessen the current concentration. In other words,it needs to be increased to a resistance equivalent to the anode-cathoderesistance during normal operation. That is, the following expressionhas to be satisfied:

(resistance of leak prevention layer when taking on a highresistance)≧(resistance of organic functional layer at ordinarytemperature)

To what extent the resistance of the leak prevention layer should changein the process of shifting from ordinary temperatures to highresistances cannot be said unconditionally, because it depends on thestructure of the element, but in general, it is preferable that theresistance is increased by at least one order of magnitude, or becomesinsulating (specific resistance of at least 10¹¹ Ω·cm) when taking on ahigh resistance.

The leak prevention layer prevents breakdown of the organic EL elementcaused by defect portions formed unintentionally in other layersconstituting the organic functional layer. Consequently, there shouldnot be any defects in the leak prevention layer itself. However, whenthere are uneven portions due to scratches or foreign matter on thesubstrate, then common defects occur easily in the layers constitutingthe organic functional layer, so that there is the possibility thatdefects occur in the leak prevention layer itself. If a large number ofdefects occur in the leak prevention layer, then it may not be capableof preventing shorts even when taking on a high resistance due to Jouleheat.

Considering the above, it is preferable that the leak prevention layerhas a step coverage that is as least as good as that of the otherorganic functional layers, and that it has few pinholes. In order toform a film with good step coverage and few pinholes, it is preferableto form the leak prevention layer by a wet film formation process, suchas spin-coating or printing, or by a vapor-phase film formation processwith good wraparound, such as CVD.

Furthermore, if the leak prevention layer is fabricated by a filmformation process with high directionality and poor step coverage, suchas vapor deposition, then it is preferable to provide the film with goodstep coverage by after-processing.

Here, “spin-coating” refers to methods of dropping a flowable materialonto a rotating layering surface, and applying that material uniformlyon the layering surface by centrifugal force. Furthermore, “printing”refers to methods such as flexography.

Furthermore, “CVD (chemical vapor deposition)” refers to methods inwhich a vapor of the molecules of a reaction system or a mixed vapor ofsuch molecules and an inactive carrier is flowed onto a heatedsubstrate, and the reaction product from a reaction such as hydrolysis,autolysis, photolysis, oxidation-reduction, or substitution is depositedon the substrate.

Furthermore, “vapor deposition” refers to methods in which small piecesof metal or non-metal are evaporated by heating in a high vacuum, andquasi-adhered as a thin film on a primer surface, such as glass, aquartz plate, a cleaved crystal or the like.

FIGS. 6A and 6B show an example of an after-treatment process forimproving the step coverage of a leak prevention layer formed by vapordeposition. As shown in FIG. 6A, when a film formation process with poorstep coverage, such as vapor deposition, is used, then the leakprevention layer is formed on the upper surface of protrusions and thebottom surface of depressions, but the leak prevention layer isdifficult to form at the lateral surfaces of the protrusions anddepressions. For this reason, the layer below the leak prevention layeris exposed, and it is difficult to completely cover the layer below itcompletely with the leak prevention layer.

In order to correct this deficiency, the leak prevention layer is heatedin an after-treatment to a temperature close to the glass transitionpoint or melting point of the material constituting the leak preventionlayer. Due to this heating, the leak prevention layer is melted andshifted, covering the exposed layer below it. Thus, the surface of theleak prevention layer is smoothened, pinholes are eliminated, and itbecomes possible to improve its step coverage.

Here, if the leak prevention layer is thick, then there are few pinholesand the step coverage is good, so that it is possible to attain a filmwith few defects. Also, the resistance of the leak prevention layer inthe film thickness direction is proportional to the product of specificresistance and film thickness of the leak prevention layer, so that ifthe leak prevention layer is thick, the effect of taking on a highresistance due to high temperatures at defect portions is even morepronounced, which is preferable.

However, if the leak prevention layer is thick and its resistance infilm thickness direction becomes large, then the driving voltage of theelement at ordinary portions is increased. Moreover, if the leakprevention layer is formed such that it is common to and there is fullcontact between adjacent pixels, then, if the film thickness of the leakprevention layer is too thick, the resistance in horizontal direction(sheet resistance) of the leak prevention layer becomes small, and thereis the possibility that adjacent pixels becomes electrically shorted.The sheet resistance of the leak prevention layer is proportional to(specific resistance/film thickness).

If the leak prevention layer is thin, then the resistance of the leakprevention layer in film thickness direction becomes small, and thedriving voltage of the element at ordinary portions is decreased.However, if the leak prevention layer is thin, there are more pinholes,and the step coverage becomes poor, so that the film will contain manydefects. Furthermore, the resistance of the leak prevention layer in thefilm thickness direction becomes small, so that there is the possibilitythat the effect of taking on a high resistance due to high temperaturesat defect portions becomes small.

Considering the above, as a lower limit for the thickness of the leakprevention layer it is preferable that the resistance in thicknessdirection of the leak prevention layer after it has taken on a highresistance at high temperatures is set to be larger than the resistancein thickness direction of the organic functional layer in the regularportions (outside the leak prevention layer). Furthermore, it ispreferable that the leak prevention layer is so thick that no defectsoccur in it. As a range fulfilling these conditions, it is preferablethat the film thickness of the leak prevention layer is for exampleabout 100 Å.

Furthermore, if the leak prevention layer is formed such that it iscommon to and there is full contact between adjacent pixels, then it ispreferable that adjacent pixels are not shorted and no cross-talkoccurs. The range fulfilling this condition depends on the size of thegap between adjacent pixels, but to be specific, the sheet resistance ofthe leak prevention layer is preferably at least 1 MΩ·cm, morepreferably at least 10 MΩ·cm, and even more preferably at least 100MΩ·cm.

As a material for the leak prevention layer fulfilling these conditions,it is possible to use a polymer material whose conductivity has beenincreased by doping it with an acid. More specifically, it is possibleto use a conductive polymer, such as polyaniline, polypyrrole,polythiophene or polyfuran. These polymers may be doped with an acid inorder to elevate their conductivity. When these polymers are heated to ahigh temperature, the doped acid is de-doped, and their resistanceincreases, so that their conductivity decreases. These materialsordinarily can be formed into a film by spin-coating or printing.

As acids with which these polymers can be doped, it is possible to useinorganic acids, such as hydrochloric acid, sulfuric acid or nitricacid, or acetic acid, formic acid or oxalic acid.

It is also possible to use an organic semiconductor that takes on a highresistance by thermally decomposing as the material for the leakprevention layer. More specifically, it is possible to use an organicsemiconductor such as a TCNQ (7,7,8,8-tetracyanoquinomethane) complex.When this type of organic semiconductor is heated to a high temperature,it thermally decomposes and takes on a high resistance. With thesematerials, it is possible to form films by vapor deposition. After thefilm has been formed by vapor deposition, it is possible to decreasedefects such as pinholes and to improve its step coverage by subjectingit to a heating treatment, as described above.

Modified Embodiment

A modified embodiment of the present invention will now be described.

In the above-described embodiment, a structure was shown in which theanode is formed on the substrate, but the present invention is notlimited thereto, and it can also be applied to structures in which thecathode is formed on the substrate. An example of this is depicted as amodified embodiment in FIG. 7.

In the organic EL element in FIG. 7, a cathode 32 is formed on asubstrate 31, and layered on top thereof is an organic functional layer34 including, in that order, an electron injection layer 35, alight-emitting layer 36, a hole transport layer 37 and a hole injectionlayer 38. An anode 33 is formed on the hole injection layer 38.

In the organic EL element in FIG. 7, the electron injection layer 35functions as an electron injection layer for injecting electrons intothe light-emitting layer 36 in an ordinary working temperature region,and functions as a leak prevention layer suppressing excessive currents.The electron injection layer 35 is made of a material whose specificresistance increases at least in a high temperature region that exceedsthe maximum working temperature of the product (maximum operatingtemperature or maximum storage temperature), thus taking on a highresistance. Consequently, the electron injection layer 35 takes on ahigh resistance by the generation of Joule heat due to currentconcentration caused by defects. Thus, the current is curbed, and theelement can be protected from such damage as dielectric breakdown.

FIG. 8 shows another modified embodiment of the present invention. Inthe organic EL element in FIG. 8, a cathode 42 is formed on a substrate41, and layered on top thereof is an organic functional layer 44including, in that order, an electron injection layer 45, alight-emitting layer 46, a hole transport layer 47 and a hole injectionlayer 48. An anode 43 is formed on the hole injection layer 48.

In the organic EL element in FIG. 8, the electron injection layer 45functions as an electron injection layer for injecting electrons intothe light-emitting layer 46 in an ordinary working temperature region,and also functions as a leak prevention layer suppressing excessivecurrents. Furthermore, the hole injection layer 48 functions as a holeinjection layer for injecting holes into the light-emitting layer 46 inan ordinary working temperature region, and also functions as a leakprevention layer suppressing excessive currents. The electron injectionlayer 45 and the hole injection layer 48 are made of materials whosespecific resistance increases at least in a high temperature region thatexceeds the maximum working temperature of the product (maximumoperating temperature or maximum storage temperature), thus taking on ahigh resistance. Consequently, the electron injection layer 45 and thehole injection layer 48 take on a high resistance by the generation ofJoule heat due to current concentration caused by defects. Therefore,the current is curbed, and the element can be protected from such damageas dielectric breakdown. It is thus also possible to provide the organicfunctional layer with two or more leak prevention layers.

The following is an explanation of a manufacturing method of theembodiments of the organic EL element according to the presentinvention. However, it should be noted that the present invention is notlimited to the examples described below.

EXAMPLE 1

In Example 1, an organic EL element was fabricated with the followingprocedure.

(1) Anode Formation

An ITO film of 1500 Å thickness was formed by sputtering on a glasssubstrate. Then, the photoresist AZ6112 (by Tokyo Ohka Kogyo, Co., Ltd.)was patterned on the ITO film. The resulting substrate was immersed in amixture of a ferric chloride aqueous solution and hydrochloric acid, andthe portion of the ITO not covered by the resist was etched away. Afterthat, the glass substrate was immersed in acetone to remove the resist,thus obtaining a predetermined ITO electrode pattern.

(2) Formation of Leak Prevention Layer

A coating liquid of a polyaniline derivative doped with acid dissolvedin an organic solvent was spin-coated onto the glass substrate of (1).The coating liquid adhering to terminal portions outside the displayportion of the substrate was removed by wiping it off, and then thesubstrate was heated with a hot plate to evaporate the solvent, thusobtaining a polyaniline film (leak prevention layer) of 450 Å thickness.

(3) Formation of Other Organic Functional Layers and Cathode

A NPABP film of 250 Å and an Alq3 film of 600 Å thickness were formed byvapor deposition on the glass substrate of (2) as the organic functionalfilms besides the leak prevention layer. Furthermore, an Al—Li alloyfilm of 1000 Å thickness was formed by vapor deposition as the cathode,thus concluding the organic EL element. The size of the organic ELelement defined by the intersection of anode and cathode was 2 mm×2 mm.

COMPARATIVE EXAMPLE 1

As Comparative Example 1, an organic EL element was prepared in the samemanner as in Example 1, except that Step (2) of Example 1 was notperformed (that is, no leak prevention layer was formed), and the filmthickness of the NPABP in Step (3) was set to 700 Å. The organic ELelement of Example 1 and the organic EL element of Comparative Example 1had the same total film thickness.

(Specific Resistance of the Polyaniline Derivative Film)

A polyaniline film was formed on glass substrates in the same manner asin Step (2) of Embodiment 1, thus preparing samples. These samples wereheated for 5 min with a hot plate to various temperatures. The sheetresistance of the heated samples was measured by the two-terminalmethod, and their film thickness was measured with a Dektak stylusprofilometer, and their respective specific resistance was determinedfrom the measurement results.

FIG. 9 is a graph showing the relation between the heating temperatureand the specific resistance of the polyaniline film. At 250 to 300° C.,the specific resistance of the polyaniline derivative film increasesroughly by a factor of 100. It seems that this is a result of the dopedacid being de-doped due to heat, leading to a sharp increase inresistance. Thus, at a temperature region of 250 to 300° C., theresistance of this polyaniline film increases sharply to take on a highresistance, showing that the polyaniline film is suitable as a leakprevention layer.

(Inverse Properties of the Element)

A reverse voltage (anode to minus and cathode to plus) was applied tothe elements fabricated in Example 1 and Comparative Example 1, and thecurrent flowing through the elements was measured. The measurement wascarried out twice per sample. The measurement results are shown in FIG.10.

In the element of Example 1, a rise in current can be observed thatappears to be caused by shorts between anode and cathode near 3 V and 5V at the first measurement, but the current immediately returns tonormal values. It seems that a large current temporarily flowed atdefect portions, but the effect of the leak prevention layer lessenedthe current concentration. At the second measurement, no rise in currentcould be observed, and smooth characteristics with small current valuesare attained. It seems that this is because the defect portions thatappeared when a voltage was applied for the first time were repaired bythe leak prevention layer.

On the other hand, in the element of Comparative Example 1, there is arise in current at both the first and the second measurement thatappears to stem from shorts between anode and cathode, and there is nosign that the defects are repaired. Thus, it was found that thebreakdown of the element due to current concentrations is prevented byproviding a leak prevention layer.

EXAMPLE 2

An organic EL display panel was manufactured with the followingprocedure.

(1) Anode Formation

An ITO film of 1500 Å thickness was formed by sputtering on a glasssubstrate. Then, the photoresist AZ6112 (by Tokyo Ohka Kogyo, Co., Ltd.)was patterned on the ITO film. The resulting substrate was immersed in amixture of a ferric chloride aqueous solution and hydrochloric acid, andthe portion of the ITO not covered by the resist was etched away. Afterthat, the glass substrate was immersed in acetone, to remove the resist,thus obtaining a stripe-shaped electrode pattern made of 256 lines.

(2) Formation of Leak Prevention Layer

A coating liquid of a polyaniline derivative doped with acid dissolvedin an organic solvent was spin-coated in the glass substrate of (1). Thecoating liquid adhering to terminal portions outside the display portionof the substrate was removed by wiping it off, and then the substratewas heated with a hot plate to evaporate the solvent, thus obtaining apolyaniline film (leak prevention layer) of 450 Å thickness.

(3) Formation of Other Organic Functional Layers and Cathode

A NPABP film of 250 Å and an Alq3 film of 600 Å thickness were formed byvapor deposition on the glass substrate of (2) as the organic functionalfilms besides the leak prevention layer. Furthermore, an Al—Li alloyfilm of 1000 Å thickness was formed by vapor deposition as the cathode,using a mask made of a striped pattern with 64 stripes. The size of onedot defined by the intersection of anodes and cathodes was 0.3 mm×0.3mm, and there were 256×64 dots.

(4) Sealing

Under a dry nitrogen atmosphere, a sealing plate having a desiccantfixed to its depression portions was laminated with an adhesive againstthe substrate of Step (3), thus forming a passively driven organic ELdisplay panel.

COMPARATIVE EXAMPLE 2

As Comparative Example 2, an organic EL panel with 256×64 dots wasprepared in the same manner as in Example 2, except that Step (2) ofExample 2 was not performed (that is, no leak prevention layer wasformed), and the film thickness of the NPABP was set to 700 Å. Theorganic EL elements of Example 2 and the organic EL elements ofComparative Example 1 had the same total film thickness.

(High-Speed Continuous Driving Test)

The panels fabricated in Example 2 and Comparative Example 2 wereconnected to a predetermined driving circuit, and after operating themcontinuously for 500 hours under a 85° C. atmosphere, the number of dotsthat have become defective as a result of shorts between anode andcathode were counted. The results were as follows:

Panel of Example 2: Number of Defect Dots: 0

Panel of Comparative Example 2: Number of Defect Dots: 16

Consequently, it was confirmed that in the panel of Example 2, which hasa leak prevention layer, there were fewer defects due to shorts than inthe panel of Comparative Example 2, which does not have a leakprevention layer.

As described above, an organic EL element according to an embodiment ofthe present invention includes an anode, a cathode, and a light-emittingorganic EL layer sandwiched between the anode and the cathode, theorganic EL layer having at least a leak prevention layer that takes on ahigh resistance when its temperature is increased. Consequently, evenwhen there is an excessive current caused by defects in the organicfunctional layer, the leak prevention layer takes on a high resistanceas a result of the heat generated by the excessive current, and thecurrent is curbed, so that element breakdown caused by defects of theorganic EL element can be prevented before it occurs.

Furthermore, the step coverage of the leak prevention layer is made atleast equivalent to that of the other layers, so that the leakprevention layer can cover defect portions in the organic functionallayer, and the effect of the present invention can be improved evenfurther.

1-12. (canceled)
 13. An organic EL element comprising an anode, acathode, and a light-emitting organic EL layer sandwiched between saidanode and said cathode, wherein said organic EL layer comprises a leakprevention layer that takes on a high resistance when its temperature isincreased.
 14. The organic EL element according to claim 13, whereinsaid leak prevention layer has hole transport abilities, and transportsholes from the anode side to the cathode side.
 15. The organic ELelement according to claim 13, wherein said leak prevention layer haselectron transport abilities, and transports electrons from said cathodeside to said anode side.
 16. The organic EL element according to claim14, wherein said leak prevention layer has electron transport abilities,and transports electrons from said cathode side to said anode side. 17.The organic EL element according to claim 13, wherein said leakprevention layer is arranged in contact with said anode.
 18. The organicEL element according to claim 14, wherein said leak prevention layer isarranged in contact with said anode.
 19. The organic EL elementaccording to claim 13, wherein said leak prevention layer is arranged incontact with said cathode.
 20. The organic EL element according to claim15, wherein said leak prevention layer is arranged in contact with saidcathode.
 21. The organic EL element according to claim 13, wherein saidleak prevention layer takes on a high resistance at temperatures of atleast 120° C.
 22. The organic EL element according to claim 21, whereinsaid leak prevention layer takes on a high resistance at temperatures of120 to 400° C.
 23. The organic EL element according to claim 22, whereinsaid leak prevention layer takes on a high resistance at temperatures of200 to 300° C.
 24. The organic EL element according to claim 13,wherein, when taking on a high resistance, the specific resistance ofsaid leak prevention layer increases at least by a factor of
 10. 25. Theorganic EL element according to claim 13, wherein, when taking on a highresistance, the specific resistance of said leak prevention layerbecomes at least 10¹¹ Ω·cm.
 26. The organic EL element according toclaim 13, wherein said leak prevention layer comprises a conductivepolymer that is doped with an acid.
 27. The organic EL element accordingto claim 13, wherein said leak prevention layer is made by a wet filmformation process or a vapor-phase film formation process.
 28. Theorganic EL element according to claim 14, wherein said leak preventionlayer takes on a high resistance at temperatures of at least 120° C. 29.The organic EL element according to claim 15, wherein said leakprevention layer takes on a high resistance at temperatures of at least120° C.
 30. The organic EL element according to claim 16, wherein saidleak prevention layer takes on a high resistance at temperatures of atleast 120° C.
 31. The organic EL element according to claim 17, whereinsaid leak prevention layer takes on a high resistance at temperatures ofat least 120° C.
 32. The organic EL element according to claim 18,wherein said leak prevention layer takes on a high resistance attemperatures of at least 120° C.